This research examines the impact of aging on plasma free and sulfconjugated catecholsmines at rest and during exercise stress. Furthermore, the impact of exercise training in those measures will be determined. Sulfoconjugation is an important deactivation mechanism for free catecholamines (CA) released from the sympathetic nervous system and adrenal gland. Low sulfoconjuration of free CA has been linked to essential hypertension. Advancing chronological age is characterized by augmented plasma free CA concentrations at rest and during physical exertion, due to heightened appearance rate and reduced clearanced. To date no study has examined whether the reduced clearance of CA in older individuals is due in part to low sulfoconjugation relative to free amine appearance rates. To address this issue, 20 healthy males aged 30-40 yrs and 20 healthy males aged 55-65 yrs will be examined at rest and during 15 min. of submaximal exercise (70% V02 max). The age groups will be further categorized into high-fit (45-55 ml.kg-1 min-1) and moderate-fit (25-35 ml.kg-1 min-1). Plasma free and sulfoconjugated CA profiles will be examined determine any age effect and any age x cardiovascular fitness interaction. Additionally, 10 experimental males (aged 55-65 yrs) will undergo a 12 wk exercise training program and be compared to controls to identify adaptations occurring with free CA, their sulfoconjugates, and the ratio of free to sulfocnonjugated CA. This research has importance in terms of 1) determining whether reduced sulfoconjugation is one mechanism by which clearance of CA is compromised with advancing chronological age, 2) identifying whether the postulated low sulfoconjugation ability with advanced age is attenuated by maintaining a high level of cardiovascular fitness, and 3) examining whether an intervention program designed to increase cardiovascular fitness and resulting in chronically enhanced perfusion of tissue high in phenosulfotransferase activity stimulates reduced free plasma CA with increased sulfoconjugation, thus reflecting a more desireable ratio between the active and inactive forms. This research provides further understanding of neuroendocrine processes with advancing chronological age, and offers insight into the potential importance of cardiovascular fitness and exercise training for maintaining neuroendocrine functioning.